Hyundai Yanmar TNV Series Manual page 53

CONTROL SYSTEM
Rack actuator output
The rack actuator output is a high-side output. See Figure 2-21.
The E-ECU adjust the magnitude of current flowing through the rack actuator solenoid by shortening or
lengthening the ON-duration of the output transistor. The rack position of the fuel injection pump varies
depending on the magnitude of current flowing through the rack actuator.
This technique where the ON duration of the transistor is changed to provide current control is called PWM
(Pulse Width Modulation). The PWM control period of the Eco-governor E-ECU is 0.4 ms.
EGR valve output
The EGR valve output is a high-side output. See Figure 2-22.
The EGR valve is driven by a stepping motor. This stepping motor adopts two-phase excitation and requires
holding current to keep the valve stopped. "Two-phase excitation" means that the solenoid is supplied with
two-phase current and "holding current" does that the solenoid is always energized. The motor of the EGR
valve is consequently approx. 24 watt heated even while the engine is at rest.
The E-ECU turns on or off the output transistors in the sequence shown in Figure 2-22, thereby driving the
solenoids for the stepping motor and opening/closing the EGR valve. The speed of the valve open/close
operation depends on the on/off speed of the transistors. The EGR valve opens at 125 pps (pulses per
second: the number of steps taken per second) and closes at 250 pps (20 pps for 10 steps before full close).
2-34
ECU
PWM output
0.4ms
Short
Long
Figure 2-21 Rack actuator output
VB
ECU
A
VB
A
VB
B
B
VB
ERG valve motor
(Stepping motor)
B
Figure 2-22 EGR valve driving mechanism
VB
Rack actuator
Small current
Large current
Motorized valve operation
Open (counterclockwise)
Step
A
A
A
B
B
B
Close (clockwise)
Step
A
A
A
B
B
TNV Application Manual